Metering roller for a lithographic printing press

Abstract

A method for maintaining, without using alcohol, a uniform film of dampening fluid on a lithographic printing press dampening roller. Said roller comprises a resilient surface with grooves helically formed about the roller surface. Said roller is positioned in a pressure indented relation to a smoothly finished transfer roller having a hydrophilic surface, creating an area of differential pressure along said grooves at the point of contact, or nip, between the rollers. Upon rotation of the rollers, excess water is transferred to the low pressure regions near the grooves of the nip and then to the end of the roller where it is returned to the dampening fluid pan.

Having described my invention, I claim: 
     
       1. A method of applying dampening fluid which is essentially free of alcohol to a printing plate in a lithographic printing press comprising the steps of: urging surfaces of a metering roller and a transfer roller into pressure indented relation to form a metering nip;   rotating said transfer roller and said metering roller such that dampening fluid is carried by the surface of at least one of the rollers through said metering nip;   forming a zone of differential pressure intermediate opposite ends of said metering nip;   moving said zone of differential pressure longitudinally of said metering nip for transferring a portion of the dampening fluid longitudinally of said metering nip toward the end of said rollers to form a spiral shaped bead of dampening fluid on the surface of one of the rollers at said metering nip; and   slipping the surface of the roller having said spiral shaped bead relative to a form roller for moving the bead of dampening fluid through a second nip to apply a uniform film of dampening fluid to said form roller.   
     
     
       2. The method of claim 1, the steps of forming a zone of differential pressure comprising the steps of: urging a resilient surfaced roller having a groove formed in the surface thereof into pressure indented relation with a hydrophilic surface; and   rotating said resilient surfaced metering roller such that the portion of the groove in the resilient roller surface in the metering nip moves longitudinally of said nip upon rotation of said metering roller.   
     
     
       3. A dampening system for a lithographic printing press comprising: a pair of rollers mounted for rotation about spaced axes, at least one of said rollers having a resilient cover and a resilient surface;   means urging surfaces of said rollers into pressure indented relation to form a metering nip;   means supplying liquid to said metering nip; and   means rotating one of said rollers such that adjacent surfaces of said rollers meter a film of liquid through said metering nip, said resilient cover having a helical groove formed therein, said helical groove being angularly inclined relative to the axis of the roller, such that adjacent areas of differential pressure are formed longitudinally of said metering nip upon movement of said resilient surface through said metering nip to transfer an effective amount of the liquid to form a spiral shaped bead of dampening fluid on one of the rollers.   
     
     
       4. A dampening system for a lithographic printing press according to claim 3, one of said pair of rollers comprising: a transfer roller having a smooth hydrophilic surface.   
     
     
       5. A dampening system for a lithographic printing press according to claim 3, at least one of said pair of rollers comprising: a metering roller having a rigid tubular core, said resilient cover being formed on said rigid tubular core of said metering roller, said resilient cover being formed of material having a Shore A durometer in a range of 18 to 30.   
     
     
       6. A dampening system for a lithographic printing press according to claim 5, said cover having a thickness in a range of 1/8 to 3/4 inch. 
     
     
       7. A dampening system for a lithographic printing press according to claim 3, said means rotating one of said rollers such that adjacent surfaces of said rollers meter a film of liquid through said metering nip comprising: drive means rotating said rollers at different surface speeds such that slippage occurs between adjacent surfaces of said rollers in said metering nip.   
     
     
       8. A dampening system for a lithographic printing press according to claim 3, said means urging surfaces of said rollers into pressure indented relation to form a metering nip; comprising: means for adjusting pressure between adjacent surfaces of said rollers in said metering nip.   
     
     
       9. A dampening system for a lithographic printing press according to claim 3, said means supplying liquid to said metering nip comprising: a pan containing dampening fluid, said pan being positioned such that a surface on one of said rollers dips into the dampening fluid.   
     
     
       10. A dampening system for a lithographic printing press according to claim 8, said means supplying liquid to said metering nip comprising: a pan containing dampening fluid, said pan being positioned such that a surface on one of said rollers dips into the dampening fluid.   
     
     
       11. A dampening system for a lithographic printing press comprising: a transfer roller having a hard hydrophilic surface;   a metering roller having a resilient surface, the surface of at least one of said rollers having a smooth continuous groove extending spirally around said one roller surface, said groove having ends terminating adjacent opposite ends of said one roller;   means urging spaced portions of the bottom surface of said spiral groove into pressure indented relation with said hard hydrophilic surface to form a metering nip such that the profile of the magnitude of pressure across the width of the portion of the groove which is urged into pressure indented relation with said hydrophilic surface along the length of said bottom surface is substantially uniform and such that pressure along the length of said metering nip between said portions of said groove is substantially uniform to form spaced zones of differential pressure along said metering nip.